[moderation] [serial?] KCSAN: data-race in n_tty_write / tty_set_termios (14)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e53642b87a4f Merge tag 'v6.18-rc3-smb-server-fixes' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16938342580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=7d996c9d5c6410002891
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/11dffeeb809f/disk-e53642b8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c9676883f34a/vmlinux-e53642b8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ae88632bdb7f/bzImage-e53642b8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7d996c...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_write / tty_set_termios

write to 0xffff888104283508 of 44 bytes by task 10163 on cpu 0:
tty_set_termios+0xc0/0x8c0 drivers/tty/tty_ioctl.c:335
set_termios+0x35b/0x4d0 drivers/tty/tty_ioctl.c:516
tty_mode_ioctl+0x379/0x5c0 drivers/tty/tty_ioctl.c:-1
n_tty_ioctl_helper+0x91/0x210 drivers/tty/tty_ioctl.c:982
n_tty_ioctl+0x101/0x200 drivers/tty/n_tty.c:2509
tty_ioctl+0x83f/0xb80 drivers/tty/tty_io.c:2801
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x1816/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888104283514 of 4 bytes by task 10162 on cpu 1:
n_tty_write+0x9f/0xb40 drivers/tty/n_tty.c:2354
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write+0x378/0x690 drivers/tty/tty_io.c:1081
tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x52a/0x960 fs/read_write.c:686
ksys_write+0xda/0x1a0 fs/read_write.c:738
__do_sys_write fs/read_write.c:749 [inline]
__se_sys_write fs/read_write.c:746 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:746
x64_sys_call+0x2802/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00008a3b -> 0x00000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10162 Comm: syz.0.2443 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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